In the operation of a conventional gas turbine, intake air from the atmosphere is compressed, heated by a compressor and caused to flow to a combustor where fuel is mixed with the compressed air and the mixture is ignited and burned. The heat energy thus released then flows in the combustion gases to the turbine where it is converted into rotary mechanical energy for driving equipment, such as for generating electrical power or for running an industrial process. Use of a combustion catalyst in the combustion zone is known to promote complete combustion of lean premixed fuels and thereby minimize undesirable emissions. Typical combustion catalysts for a hydrocarbon fuel-oxygen reaction include platinum, palladium, rhodium, iridium, terbium-cerium-thorium, ruthenium, osmium and oxides of chromium, iron, cobalt, lanthanum, nickel, magnesium and copper, for example.
Noble elements such as platinum or palladium are commonly used catalytic combustion surfaces in a catalytic combustor of a gas turbine. However, such noble elements may not be sufficiently durable above certain temperatures and may not offer sufficient insulating properties to protect a metallic substrate from elevated temperature attack such as corrosion or oxidation. Further, wash coats of catalytic materials can erode, spall or otherwise wear away from an underlying thermal barrier coating or substrate over time and the catalytic material may become deactivated. These events lead to inefficient combustion and typically require new coatings or maintenance.
U.S. Patent Application Publication U.S. 2003/0056520 A1, which is specifically incorporated herein by reference, discloses a catalyst element that includes a substrate, a thermal barrier coating disposed over the substrate and a combustion catalyst disposed over the thermal barrier coating. A ceramic wash-coat may be disposed between the thermal barrier coating and the catalyst. In order to obtain a desired more turbulent flow of fuel-air mixture, the thermal barrier coating surface has at least one feature suitable to interdict the flow and cause the flow to become more turbulent than if such feature did not exist.